1. Field of the Invention
The present invention relates to an apparatus for converting a screen aspect ratio, and particularly to an improved apparatus for converting a screen aspect ratio, which is capable of horizontally compressing a 4:3 video signal and horizontally extending a 2:1 video signal by varying the scanning line of a screen, when a wide screen television having a 16:9 aspect ratio receives a 4:3 video signal or a 2:1 video signal.
2. Description of Related Art
Generally, in the national television system committee (NTSC) and the phase alternating line (PAL), a letter box type signal is transmitted by forming a low band image as much as 3/4 of the original active region (the effective image region) and blacking the upper and lower portions or the left- and right-side portions of the screen of the television.
The transmission of the letter box signal is directed to displaying the image having a screen aspect ratio of 16:9 on the screen of the television having a 4:3 screen aspect ratio without torsion of the image.
However, as the wide screen television having a screen aspect ratio of 16:9 is introduced, it is needed to display the image of a screen aspect ratio of 4:3 on the wide screen television having a screen aspect ratio of 16:9.
Therefore, the television broadcasting station concurrently transmits a 4:3 aspect ratio program in order for the television having a function of receiving a 4:3 aspect ratio screen signal and the television having a function of receiving a 16:9 aspect ratio screen signal to selectively receive a corresponding television program transmitted from the television broadcasting station.
In addition, the television is equipped with a device for automatically detecting a wide screen signal (WSS) which is referred to the 4:3 program or the 16:9 program. Here, the screen of the television should be varied in accordance with the received signal.
However, in order to receive the 4:3 program transmitted from the television broadcasting station on the wide screen television having an aspect ratio of 16:9, it is necessary to horizontally compress the scanning line of the screen, and when receiving the 2:1 cinema signal, the scanning line of the screen should be horizontally extended.
FIG. 1 shows the conventional apparatus for converting a screen aspect ratio, which is directed to displaying the 4:3 video signal or the 2:1 cinema video signal on the wide screen television having the 16:9 screen aspect ratio.
As shown therein, there are provided a clock generator 102 for generating a clock signal CLK1 when a horizontal synchronous signal Hsy is inputted thereto through a synchronous input terminal 101 for a horizontal compression and expansion, a clock counter 103 for counting the clock signal CLK1 generated by the clock generator 102 and for outputting the counted value, an elimination image range judging unit 104 for comparing the previously set reference value with the clock counting value of the clock counter 103, eliminating as much as 1/18 of the image of the left-side and right-side image in the 16:9 screen in accordance with the comparison result, and generating a clock selection control signal S1 and a writing enable signal WE so as to display the 2:1 cinema video signal, an effective image range judging unit 105 for comparing the clock counting value of the clock counter 103 with the previously set reference value, judging the effective image range value and the horizontal scanning line range in accordance with the comparison result, and generating a clock selection control signal S2 and a side panel selection control signal SPC for horizontally compressing the image in accordance with the judging result, a frequency multiplier 106 for multiplying the clock signal CLK1 outputted form the clock generator 102 by 4/3 and for generating a clock signal CLK2, a frequency multiplier 107 for multiplying the clock signal CLK1 generated by the clock generator 102 by 8/9 and for generating a clock signal CLK3, a clock selector 108 for being switched in accordance with a control signal S1 generated by the elimination image range judging unit 104 and for selecting either the clock signal CLK1 of the clock generator 102 or the clock signal CLK3 of the frequency multiplier 107, a clock selector 109 for being switched in accordance with the clock selection control signal S2 generated by the effective image range judging unit 105 and for selecting either the clock signal CLK2 which is multiplied by 4/3 by the frequency multiplier 106 or the clock signal selected by the clock selector 108, an edge detector 110 for detecting a rising edge of the horizontal synchronous signal Hsy outputted from the synchronous input terminal 101 and for generating a reset signal RST whenever the rising edge is detected, a line memory unit 111 for being enabled in accordance with a writing enable signal WE generated by the elimination image range judging unit 104, receiving the clock signal CLK1 generated by the clock generator 102 as the writing clock signal, receiving the clock signal selected by the clock selector 108 as a reading clock signal, storing and outputting the digital image data of 8 bits inputted thereto through the image input terminal 100 at every line, being reset in accordance with the reset signal RST generated by the edge detector 110, and writing/reading the image data of the next line, a line memory unit 112 for receiving the clock signal selected by the clock selector 108 as a reading clock signal, storing and outputting the image data outputted from the line memory unit 111 at every horizontal line, being reset in accordance with a reset signal RST generated by the edge detector 110 and for writing/reading the image data of the next line, and a side panel insertion until 113 for outputting the horizontally converted digital image data through the output terminal 114 by inserting a luminance level value of a temporary side panel to the image data which is inputted thereto at every line from the line memory unit 112 in accordance with a side panel selection control signal SPC of the effective image range judging unit 105.
The operation of the conventional apparatus for converting a screen aspect ratio will now be explained with reference to the accompanying drawings.
First, the horizontal compression process of the television image will now be first described with reference to FIG. 2A.
When the horizontal synchronous signal Hsy is inputted into the clock generator 102 through the synchronous input terminal 101, the clock generator 102 generates the clock signal CLK1 whenever the horizontal synchronous signal Hsy is inputted from the synchronous input terminal 101 so as to horizontally compress the digital image data inputted thereto through the image input terminal 100 and then outputs the clock signal CLK1 to the clock counter 103, the frequency multipliers 106 and 107, the clock selector 108 and the line memory unit 111, respectively.
The frequency multiplier 106 multiplies the clock signal CLK1 inputted from the clock generator 102 by 4/3, generates the clock signal CLK2, and outputs the clock signal CLK2 to the clock generator 109.
The frequency multiplier 107 multiplies the clock signal CLK1 inputted from the clock generator 102 by 8/9 and then generates the clock signal CLK3, and outputs the clock signal CLK3 to the clock generator 108.
In addition, the clock counter 103 counts the start portion of the clock signal CLK1 inputted from the clock generator 102 at every line, and outputs the counted value to the elimination image range judging unit 104 and the effective image range judging unit 105, respectively.
The elimination image range judging unit 104 compares the value counted by the clock counter 103 with the previously set reference value so as not to eliminate the left and right sides of the image when the screen aspect ratio is 4:3, generates the clock selection control signal S1 and the writing enable signal WE in accordance with the comparison result, outputs the clock selection control signal to the clock generator 108, and outputs the clock selection control signal S1 to the line memory unit 111.
In addition, the effective image range judging unit 105 compares the counted value inputted from the clock counter 103 with the previously set reference value, and separates the horizontal scanning line range and the effective image range in accordance with the comparison result.
Namely, when reading the video signal stored in the line memory unit 112, it is necessary to make the speed of the clock signal be different by separating the range of the horizontal scanning time into one range in which the compression is needed and another range in which the compression is not needed.
The range in which the compression is not needed is referred to the range of the horizontal scanning line range in which the horizontal synchronous signal exists, so that the compression should not be conducted.
The effective image range judging unit 105 is directed to separating the horizontal scanning time range into the horizontal scanning line range and the effective image range by comparing the counted value of the clock counter 103 with the previously set reference value, outputting the clock selection signal S2 to the clock selector 109 so as to vary the reading clock speed of the line memory unit 112 in accordance with the separated result, generating the side panel selection control signal SPC and then outputting the signal SPC to the side panel insertion unit 113.
The clock selector 108 is switched in accordance with the clock selection control signal S1 outputted from the elimination image range judging unit 104, blocks the clock signal CLK3 which is multiplied by 8/9 by the reference multiplier 107, selects the clock signal CLK1 generated by the clock generator 102, and then outputs the selected clock signal to the clock generator 109 and the line memory units 111 and 112, respectively.
In addition, the clock selector 109 is switched in accordance with the clock selection control signal S2 outputted from the effective image range judging unit 105, alternately selects the clock signal CLK2 multiplied by 4/3 by the frequency multiplier 106 and the clock signal CLK1 selected by the clock selector 108 and then outputs the selected clock signal to the line memory 112.
At this time, when the digital image data is inputted through the image input terminal 100, the line memory unit 111 is enabled in accordance with the writing enable signal WE outputted from the elimination image range judging unit 104, receives the clock signal CLK1 outputted from the clock generator 102 as the writing clock, stores the digital image data of 8 bits outputted from the image input terminal 100 at every line, receives the clock signal CLK1 selected by and outputted from the clock selector 108 (namely, the writing clock of the line memory unit 111 as the reading clock), and outputs the stored image data to the line memory unit 112 at every line.
Finally, the line memory unit 111 writes and reads using the clock signal CLK1 generated by the clock generator 102, which is delayed by 1H (the horizontal scanning period). The variation of the input/output image data is not made.
Meanwhile, the edge detector 110 detects the rising edge of the horizontal synchronous signal Hsy and generates the reset signal RST whenever the edge is detected.
The line memory unit 111 is initialized in accordance with the reset signal RST generated by the edge detector 110, and the image data of the next line is written and read in the same manner as previously explained.
Meanwhile, the line memory unit 112 receives the clock signal CLK1, which is referred to the reading clock of the line memory unit 111 selected and outputted by the clock selector 108, as the writing clock, writes the image data outputted from the line memory unit 111 at every line, receives the clock signal CLK1 alternately outputted by the clock selector 109 and the second clock signal CLK2 which is multiplied by 4/3 with respect to the clock signal CLK1, performs the FIFO process with respect to the stored image data at every horizontal scanning line, and outputs the results to the side panel insertion unit 113.
Namely, in order to horizontally compress the image data into the 4:3 data, the clock selector 109 selects the clock signal which is used as the writing clock of the line memory unit 112, which is referred to as the clock signal CLK1 selected by the clock selector 108, when the clock selection control signal S2 of the effective image range judging unit 112 is referred to the horizontal scanning line so as to read the image data of the line memory unit 112, and reads the image data stored in the line memory unit 112. No variation of the image data is made at this time.
In addition, when the clock selection control signal S2 of the effective image range judging unit 105 is referred to the effective image range, the clock signal CLK2, which is multiplied by 4/3 by the first frequency multiplier 107, is selected, and the image data stored in the line memory unit 112 is read, so that as shown in FIG. 2A, in the effective image range, the aspect ratio is maintained as 4:3 in the screen having a 16:9 aspect ratio.
In addition, as shown in FIG. 2A, in the screen having a 16:9 aspect ratio, in order to insert the side panels LSP and RSP into the left-side and right-side except for the effective image range of 4:3 (namely, into the left-side and right-side of the image signal which is compressed to 4/3 ), the luminance level value of xe2x80x9c0xe2x80x9d is inserted into the left-side and right-side panels LSP and RSP in accordance with the side panel selection control signal SPC, which is generated by the effective image range judging unit 105.
Namely, the side panel insertion unit 113 selects the image data of the line memory unit 112 and then outputs the selected image data through the output terminal 114 when the side panel selection control signal SPC obtained by the effective image range judging unit 105 is referred to the effective image range, and when the side panel selection control signal SPC is not referred to the effective image range, the luminance level value of the ground voltage is selected and inserted at both sides of the effective image range, and then is outputted through the output terminal 114.
Therefore, as shown in FIG. 2A, the screen compressed to 4:3 is displayed on the screen having an aspect ratio of 16:9.
Meanwhile, in the wide screen television having an aspect ratio of 16:9, the horizontal extension (expansion) of the cinema image signal such as 2:1 is performed as follows.
First, when the digital image data inputted through the image input terminal 100 is written in the line memory unit 111 at every horizontal line as the clock signal CLK1 generated by the clock generator 102, and is read from the line memory unit 111. The reading is performed using one clock signal selected by the clock selector 108 between the clock signal CLK1 generated by the clock generator 102 and the clock signal CLK3 which is multiplied by 8/9 by the frequency multiplier 107.
Here, in the clock selector 108, a control signal for selecting the clock signal CLK1 of the clock generator 102 and the clock signal CLK3 of the frequency multiplier 107 is referred to the clock selection control signal S1 generated by the elimination image range judging unit 104.
Namely, in order to display the image such as the cinema signal of an aspect ratio of 2:1 on the screen of 16:9, as shown in FIG. 2B, the left-side and right-side of the image should be eliminated by 1/18, respectively. Here, the elimination image range judging unit 104 compares the count value from the clock counter 103 with the previously set reference value and disables the writing enable signal WE of the line memory unit 111 in the side panel ranges LSP1 and RSP1, so that the image data is not written in the line memory unit 111 for those ranges.
In addition, the clock selector 108 selects the clock signal CLK3 which is multiplied by 8/9 by the frequency multiplier 107 in accordance with the clock selection control signal S1 of the elimination image range judging unit 104 in the effective image range as similar to the horizontal compression, and reads the image data stored in the line memory unit 111.
Therefore, the image data read in the effective image range is referred to 16/18 of the original image signal, and is read by 8/9 as the clock signal CLK3, so that the left-side and right-side of the screen having an aspect ratio of 16:9 become identical.
In addition, the signal from 1/18 of the left-side and right-side written in the line memory unit 111 is not automatically read, but is reset in accordance with the rising edge of the horizontal synchronous signal Hsy inputted from the synchronous input terminal 101 (namely, in accordance with the reset signal RST generated by the edge detector 110), and then is returned to the.next line.
In addition, the effective image range judging unit 105 selects the clock signal CLK3 that the clock selector 109 selected from the clock selector 108 in accordance with the clock selection control signal S2 of the effective image range judging unit 105. That is, the effective image range judging unit 105 selects the writing clock of the line memory unit 112, reads the image data stored in the line memory unit 112, and then outputs the image data to the side panel insertion unit 113.
Namely, it is possible to read the horizontally extended scanning line using the reading clock and the writing clock of the line memory unit 112.
In addition, the side panel insertion unit 113 selects the image data read by the line memory unit 112 in accordance with the side panel selection control signal SPC outputted from the effective image range judging unit 105 and then outputs it through the output terminal 114.
Therefore, as shown in FIG. 2B, it is possible to display the cinema image signal which is horizontally extended to 2:1 on the screen having an aspect ratio of 16:9.
In order to compress or expand the image signal inputted through the image input terminal 100, two line memory units 111 and 112 are connected in series. To horizontally compress the image signal, only one the line memory unit 112 is necessary. In addition, to horizontally expand the image signal, two line memory units 111 and 112 are needed.
However, the conventional apparatus for converting a screen aspect ratio is basically directed to a horizontally compressing and extending method. Since the above-mentioned conventional art uses the clock circuit without using the digital filter, the compression ratio and extension ratio of the clock signal used in two line memory units are different from each other. Therefore, whenever the compression ratio of the clock signal becomes different, the clock signal corresponding to the speed thereof is needed, so the clock circuit including two frequency multipliers, the clock counter, the clock generator, and the like are needed. Therefore, the construction of the conventional system is complex, it is difficult to control the clock, and the operation of the conventional system is unstable.
Accordingly, it is an object of the present invention to provide an apparatus for converting a screen aspect ratio which overcomes the problems encountered in conventional apparatuses for converting a screen aspect ratio.
It is another object of the present invention to provide a screen aspect ratio conversion, which is capable of horizontally compressing and extending (expanding) two image signals by writing in or reading from two line memory units when the wide screen television having an aspect ratio of 16:9 receives a 4:3 image signal or a 2:1 cinema image signal, thus simplifying the construction of the system.
It is another object of the present invention to provide a screen aspect ratio conversion by which the system is operated more stably by horizontally compressing and extending the image using a single clock, whereby the construction of the system is simplified.
It is another object of the present invention to provide a screen aspect ratio conversion by which it is possible to variously compress and extend the image signal using a simpler construction of the system.
It is another object of the present invention to provide a screen aspect ratio conversion by which it is possible to horizontally and vertically compress and extend the image signal using a line memory instead of a sample memory and using a field memory instead of a line memory.
It is another object of the present invention to provide a screen aspect ratio conversion by which it is possible to vary the aspect ratio of the image signal using a single clock.
To achieve the above and other objects, there is provided an apparatus for converting a screen aspect ratio, which includes a clock generator for generating a clock signal whenever a horizontal synchronous signal is inputted; a clock counter for counting the clock signal of the clock generator within a predetermined range and for generating a first writing enable signal; a coefficient controller for counting the clock signal obtained by the clock generator at every sample in accordance with a coefficient selection signal contained in the horizontal synchronous signal and inputted thereto in accordance with a horizontal compressing mode and a horizontal extending mode, generating a coefficient value of a predetermined bit, selecting a coefficient value of a predetermined bit, generating a coefficient control signal of a predetermined bit, logically processing the generated coefficient value and the coefficient selection signal, and generating a first reading enable signal and a second writing enable signal; a first line memory unit for receiving a clock signal of the clock generator as a writing/reading clock signal in accordance with the first writing enable signal of the clock counter and the first reading enable signal of the coefficient controller and for writing/reading at every line the image data inputted; a sample interpolation unit for performing 4:3 or 7:8 interpolation in accordance with the current image data inputted from the first line memory unit and the previous image data and for selecting at every line the interpolated data in accordance with a coefficient control signal of a predetermined bit generated by the coefficient controller; a second line memory unit for receiving the clock signal of the clock generator as a writing/reading clock signal in accordance with the second writing enable signal generated by the coefficient controller and the previously set second reading enable signal and for writing the image data interpolated by the sample interpolation unit at every line.
It is another object of the present invention to provide a spectacle screen using an apparatus for converting screen aspect ratios.
To further achieve the above and other objects, there is provided an appratus for converting a screen aspect ratio which includes a video signal size converting unit for receiving an input video signal and outputting an output signal for a wide screen mode by adjusting a line memory and expanding or compressing the input video signal at a predetermined ratio based on a horizontal size of a screen; a spectacle video signal outputting unit for selecting a predetermined video signal from the output video signals from the video signal size converting unit, controlling a read/write operation of the line memory based on a changing degree of a horizontal size of the selected video signal and generating a digital output video signal in which the number of horizontal pixels is changed by a screen section; and control signal generating unit for generating a read enable signal enabling the field memory based on a horizontal synchronous signal and for generating selection signals according to a wide screen section, an expanded screen section and a compressed screen section and outputting the read enable signal and the selection signals to the video signal size converting unit and the spectacle video signal outputting unit.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.